Sidebilder
PDF
ePub

the world's people rice is the main article of food. In tropical Oriental countries it takes a larger place in the dietary than is occupied in the temperate zone of the Western world by wheat, rye, barley, and potatoes combined. From the standpoint of world production and consumption, therefore, rice unquestionably takes the first place among the grains.

As a bread grain, wheat is usually preferred, with rye second in favor, and barley third.

Maize and oats are important both as human food and in the feeding of farm animals.

Buckwheat, millet, and the grain sorghums (kafirs, durra) are also of considerable importance.

Rice (Oryza sativa) If the population of the entire globe be considered, rice is the most used as human food of all the grains, since it enters so largely into the dietary of the people of India, China, Japan, and other Oriental countries.

In the United States rice plays the part only of a minor cereal, but its cultivation is increasing, especially in Louisiana and Texas. Smaller areas are devoted to rice culture in the South Atlantic States and in California.

Rice has been commonly marketed in this country either (1) unhulled, i.e. with the chaffy husk still covering the kernel ; (2) “ cured,” freed from husk but not from bran; (3) polished (white). The following comparative analyses (Table 34) of rice in these three conditions are from Bulletin 13, Bureau of Chemistry, United States Department of Agriculture, except the figures for phosphorus, which have been added by the author.

It will be seen that the“ polishing” of the rice kernel removes only about one eighth of its weight but more than half of its ash constituents. The ash in both cases is composed chiefly of phosphates, about one half of the weight of ash being P2O5.

[blocks in formation]

It has been known for some time, especially in Japan and the Philippines, that a diet consisting chiefly of polished rice is likely to result in the disease beriberi, and by careful observation and experiment it was decided that rice which had been polished so as to contain less than 0.40 per cent of P20; was unsafe for use as the chief article of food, as rice often is used in those countries. The frequency with which beriberi follows a deficient diet, such as one consisting mainly of highly polished rice, and the certainty with which it can be prevented by simply substituting unpolished (also called “ cured ”') rice, shows plainly that the removal of the outer portions of the rice kernel as in the “polishing ” process results in a deficiency of some substance or substances which occur in that part of the grain and which are important for the maintenance of health. Beriberi is therefore considered typical of the “ deficiency diseases." The limit to which rice may be "refined ” without becoming markedly deficient has been determined in terms of its phosphorus content, and it is altogether probable that a diet of polished rice taken in sufficient quantity to furnish all the energy required in nutrition would fail to furnish an adequate supply of phosphorus. Experiments have shown, however,

that so far as beriberi is concerned, the deficiency of the polished rice is due more particularly to the removal of vitamin B. In rice there is a high concentration of vitamin B in the embryo, a lower concentration in the bran, and little if any in the pure endosperm. The milling of rice is likely to lower greatly its antineuritic value through a loss of the embryo but rice which is not too highly milled still has some antineuritic value. In pure white polished rice, however, the vitamin content is so far reduced that it is a disputed point whether such rice contains any vitamin B whatever. It is also practically devoid of vitamins A and C. The use of a less highly refined product known as brown or cured rice is desirable, especially when rice constitutes a large proportion of the diet.

Partly as a result of the interest aroused by the rather striking demonstration in the Philippines of the impoverishment of rice by the complete removal of the outer layers to make a white product, “cured” or “brown " rice is now being introduced in the grocery trade.

Wheat Wheat is the typical bread-making grain and the one most used for human food in the United States, in English-speaking countries generally, and in probably the greater part of Europe. The different cultivated varieties of wheat all belong to the same genus (Triticum), but not all to one species. The wheat most commonly grown in America is Triticum vulgare, and probably the next most important from our standpoint is Triticum durum, which is valuable because of its ability to resist drouth and also because of yielding a flour suited to the manufacture of macaroni. Wheat is often classified as “hard” or “soft,” as “spring” or “winter ” wheat, and also according to the locality in which it is grown.

Winter wheat is sown in the autumn in regions where the winter is not severe, and matures early in the summer. Spring

wheat, which is grown mainly in the Northwestern states, including Minnesota and the Dakotas, and in Canada, is sown in the spring and matures in the late summer. There are many varieties of both classes, and the composition and properties vary with variety and environment. As a rule, winter wheats are softer and somewhat more starchy; the spring wheats harder and slightly richer in protein. In general a rather hard wheat of more than average protein content is preferred for the manufacture of bread flour, but the wheats with most protein do not necessarily make the best flour, since the bread-making quality depends upon the nature and quantitative relationship of the proteins and not simply on the amount present.

In bulk and value of crop, wheat ranks second to corn in production in the United States, but in quantity sold from the farms and sent into commerce it ranks first among the grains.

The structure of the wheat kernel is doubtless already familiar to most readers of this book. We shall therefore not repeat the description here, and it must be understood that this paragraph is not intended as an adequate description but only as a reminder of a few of the points which are to be kept in mind when considering the production and composition of the mill products. It should also be clearly understood that Fig. 23, representing some features in the structure of the wheat kernel, is only a diagram to illustrate these few points and is not intended as a complete picture. The bran, which is actually composed of several layers, is shown at a. The square cells of the aleurone layer are shown at b, while c represents the endosperm made up chiefly of“ starch cells ” which, however, always contain protein as well as starch. The germ or embryo, d, is shown at one end of the longitudinal section, but does not appear in the transverse section, since the germ does not extend to the middle of the kernel. The deep crease extending from end to end of the wheat kernel increases the surface considerably so that the percentage of bran and of aleurone layer is larger than would otherwise be

the case. It is estimated that the bran proper (including epidermis, epicarp, endocarp, and testa) constitutes about 5 per cent, the aleurone layer about 8 per cent, the germ with its membrane about 5 per cent, and the “ starch cells" about 82 per cent of the entire grain. The “bran ” obtained in milling may contain not only the bran proper, but also the germ and more or less of the aleurone layer, depending upon the processes employed. The flour obtained in ordinary milling contains more

[graphic][ocr errors][graphic][ocr errors][subsumed][ocr errors][subsumed]

Fig. 23. — Diagram of grain of wheat, longitudinal and transverse sections.

a, bran; b, aleurone layer; c, starch cells of endosperm; d, germ.

or less of the aleurone layer, which is rich in protein and in phosphorus compounds, and most of the “starch cells ” of the original kernel. From the relative proportions in which these exist in the grain it is evident that much the larger part of ordinary white flour must consist of these starch cells, and their general nature should therefore be kept in mind. Each cell contains hundreds of starch granules of various sizes embedded in a network of protoplasmic material composed essentially of protein

« ForrigeFortsett »